(1) Field of the Invention
The present invention relates to combination locks employed on safes and vaults, and more particularly to an improvement in lock assemblies of the punch-thru type which are intended to be effective to prevent unauthorized access from being gained to the interior of the safe or vault on which the punch-thru lock assembly is employed.
(2) Description of the Prior Art
It has long been conventional practice utilize locks for purposes of regulating access to the interior of safes and vaults. One of the most common forms of locks, which is employed for this purpose, is the so-called combination lock. The latter embodies a combination dial having numbers provided thereon which, when manipulated in accordance with a pre-established sequence, causes the tumblers housed in the enclosure case of the lock to become aligned in a set pattern whereby the bolt of the lock is moved from its locking to its unlocking position thereby permitting the door of the safe or vault to be opened.
A number of different approaches have been tried down through the years in an attempt to improve the security which is afforded through the utilization of a lock on a safe or vault. Namely, a variety of methods have been devised for use with locks in an effort to render them virtually tamperproof. Notwithstanding these efforts, surreptitious entry to safes and vaults remains a serious problem which all lock manufacturers are continuously called upon to face. In this regard, quite often it is found that surreptitious entry to a safe or vault has been gained as a consequence of the lock having been defeated in some fashion.
For example, it is well-known that there exist a significant number of individuals who possess skills which make them adept at gaining access to the interior of safes or vaults by surreptitiously opening the locks with which the latter are provided. These individuals commonly employ for this purpose a technique which depends for its utilization on the application of the human senses of hearing and/or touch. More specifically, the technique which these individuals employ in this regard involves the manipulation of the combination dial of the lock in an effort to determine, be listening for the noises and/or by sensing the vibrations which are created when the tumblers of the lock are moved in response to the rotation of the combination dial, when the tumblers have become aligned in the position thereof which corresponds to the open condition of the lock. Thus, through the successful application of the aforedescribed technique such an individual is able to effect the defeat of the lock without destroying the latter or for that matter even causing any measurable damage thereto. Concomitantly, a breach is effected of the security which is designed to be provided as a consequence of the employment of the lock; namely, the paramount reason why the lock is being used at all is to provide the desired degree of security, i.e., controlled access to the interior of the safe or vault with which the lock is used. Absent the ability of the lock to provide this degree of security, very little other justification would remain which would warrant the placement of a lock on a safe or vault. It is for this reason, therefore, that all lock manufacturers must be concerned with the matter of the relative degree of ease with which any lock manufactured thereby is capable of being defeated.
One approach which some lock manufacturers have adopted in the past to effect a lessening of the likelihood that their locks could be successfully defeated through the use of the technique described in the preceding paragraph, which is dependent on its usage for a sensing of sound and/or touch, is to employ means operable to dampen the sounds that are produced when the tumblers are moved in response to rotation of the combination dial of the lock. More specifically, the object in this instance is to provide a lock which embodies means operable such that variations in sound and feel are dampened, and moreover are prevented from being usefully transmitted to the individual manipulating the combination dial of the lock. By way of illustration, one form of such a lock embodying dampening means of the aforedescribed type can be found described and illustrated in U.S. Pat. No. 3,106,083 to 17 Maynard.
Another approach which some lock manufacturers have taken to combat the susceptibility of their locks being defeated through the technique of listening to noises and/or feeling for vibration as the tumblers move is to equip the lock with time delay means. The objective here is to provide the lock with a time delay mechanism, which is operative to permit the lock to be opened only after a pre-established time period has elapsed following the setting of the tumblers of the lock for opening. One such lock equipped with a form of time delay means comprises the subject matter of U.S. Pat. No. 3,702,551 to Blizard.
In addition to the technique described previously herein, which relies on an individual's ability to detect through sound and/or touch when the tumblers of the lock have become aligned in their open condition, there exists another technique for surreptitiously opening a lock which also is frequently employed by those seeking to gain unauthorized access to the interior of a safe or vault. Reference is had here to the technique of punching out the spindle with which the combination dial as well as the tumblers of the lock are cooperatively associated. Namely, what is done is to force the spindle out through the back of the lock, whereby the tumblers of the lock as well as the cover of the lock case are forced from, i.e., disassociated from the lock. When this occurs, the lock is rendered inoperative, such that the lock is no longer effective to perform its locking function. Thus, the door of the safe or vault can now be opened so as to enable an unauthorized person to remove the contents of the safe or vault at will. A need has therefore been demonstrated to provide a lock embodying means which is effective to overcome the ability of the lock to be mechanically defeated by removing the dial and punching-thru the spindle.